Re: [rtcweb] A few questions on draft-ejzak-dispatch-webrtc-data-channel-sdpneg-00

Paul Kyzivat <> Tue, 25 February 2014 22:22 UTC

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Date: Tue, 25 Feb 2014 17:22:48 -0500
From: Paul Kyzivat <>
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Subject: Re: [rtcweb] A few questions on draft-ejzak-dispatch-webrtc-data-channel-sdpneg-00
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On 2/25/14 12:51 PM, Christer Holmberg wrote:
> Hi Paul,
>>> My question was regarding the re-transmission values etc.
>>> Why do the peers need to negotiate those? Why would an intermediary need to know about
>>> those? Why not simply define those in the protocol description, and each endpoint supporting the >> protocol will then know what values to use?
>> IIUC, the webrtc people are "humoring* us by making provision for registered subprotocol names, > and using SDP to negotiate channels. I suspect that for the most part they have no intention of
>> using those.
>> (The subprotocol name is *optional*.)
>> So these parameters are needed to properly initialize a channel when the subprotocol is not
>> specified.
> Why would someone NOT specify the subprotocol?

Because there is no defined subprotocol for what they are doing?

In the common webrtc use case with two browsers talking to the same web 
service, and the web service feeding the needed javascript to the 
browsers, they just "know" the protocol they are using. So they may just 
"make it up", and have nothing registered.

It is when they need to interoperate with something else that it becomes 
important to name and register the protocol.

> Especially considering Richard's draft, I thought the whole idea was to be able to negotiate the subprotocol using SDP.

That's for us, not them. :-)

They will be using DCEP.

>> Also, we still have an open question about what attributes must be present in a subprotocol
>> specification. It is at least possible that some subprotocols may work with a variety of settings of
>> these attributes.
> Well, in that case the subprotocol specification should define the additional SDP attributes needed.
>> This draft should probably say more about this. It could say that:
>> * the SDP MUST be consistent with the attributes specified in the subprotocol definition, OR
>> * the SDP MUST NOT specify attributes specified in the subprotocol definition, OR
>> * attributes specified in the SDP override those specified in the subprotocol definition.
> If people see a need for these attributes, fine. But, I still have not seen an example where it would be needed (e.g. the UDP RFC does not specify the timers for SIP - RFC 3261 does :)

I was talking in general. The answers may be different for each attribute.